Evaluating the effect of dissolved oxygen on simultaneous nitrification and denitrification in polyurethane foam contact oxidation reactors

The effects of dissolved oxygen on simultaneous nitrification and denitrification were evaluated in polyurethane foam contact oxidation reactors in a municipal wastewater treatment process. It was observed that nitrate could be removed at low dissolved oxygen levels, but the removal rate was gradually reduced as the dissolved oxygen concentration increased to a higher level of 6.0 mg/L. Nitrogen removal remained optimal within the dissolved oxygen range of 0.5 to 1.0 mg/L. Denaturing gradient gel electrophoresis (DGGE) analysis revealed that the diversity of the microbial community changed accompanying dissolved oxygen values of 0.5 to 1.0 mg/L, 2.5 to 3.5 mg/L, 6.0 to 6.5 mg/L, and 10.0 to 12.0 mg/L, in turn, which was supported by the Shannon-Wiener index of 1.56, 1.71, 1.43, and 1.56, accordingly. Both DGGE profiling and phylogenetic analysis confirmed that the nitrifiers in reactors that are responsible for nitrification during the experiment include Nitrosospira sp., Nitrosomonas sp., and Nitrospira sp.